Phenol coupling initiated by one-electron oxidation of tyrosine units in peptides and histone
Prütz, W.A.; Butler, J.; Land, E.J.
International Journal of Radiation Biology and Related Studies in Physics Chemistry and Medicine 44(2): 183-196
1983
ISSN/ISBN: 0020-7616 PMID: 6603438 Document Number: 217717
Phenoxyl radicals generated pulse radiolytically by the reaction of N3 with Gly-Tyr decay bimolecularly (2k = 4.7 .times. 108 M-1 s-1) with efficient formation of 2,2'-dimers, which enolize rapidly (k = 2.7 .times. 104 s-1) to produce the 2,2'-biphenolic product. The build-up of the characteristic 2,2'-biphenol fluorescence (400 nm) and absorption also indicated a delayed (k = 80 s-1) process, probably involving the phenoxyl .tautm. phenoxy-quinol equilibrium. About 60% of the Gly-Tyr phenoxyls were found to dimerize to the 2,2'-biphenol, and a similarly efficient 2,2'-coupling seems to occur with other tyrosyls, such as Lys-Tyr-Lys and histone. .gamma.-Radiolysis was applied to estimate relative yields of formation of 2,2'-biphenols under various conditions. Dimerization is almost completely inhibited by cysteine or O2, consistent with phenoxyl repair by cysteine or .**GRAPHIC**. disproportionation of .**GRAPHIC**. with SOD prevents repair. The phenol 2,2'-coupling is less efficient for .cntdot.OH- and inefficient for .**GRAPHIC**.